The present invention relates to a drive mechanism for driving first and second displacement members disposed in tandem, and to a set for driving first and second tandems of displacement members for displacing a vehicle.
The mechanism comprises:
first and second driven sprockets respectively secured to the first and second displacement members; PA1 a hydraulic motor comprising a motor casing, a reaction member integral with the motor casing, and a cylinder block which is mounted so that the reaction member and the cylinder block rotate relative to each other about an axis of rotation, the cylinder block comprising a plurality of sets of cylinders and of pistons suitable for being fed with fluid under pressure; PA1 first and second driving sprockets which are mounted to be rotated by the hydraulic motor; and PA1 first and second chains disposed in a chain case, the first chain engaging the first driven sprocket and the first driving sprocket, while the second chain engages the second driven sprocket and the second driving sprocket.
Mechanisms of that type are already known and used to equip vehicles of the compact loader or earth mover type. Such vehicles are provided with a set of two mechanisms of the above-mentioned type, respectively for driving two right-side wheels and two left-side wheels. In this way, it is possible to guarantee that the two wheels in the same group of side wheels rotate at the same speed, but, insofar as the two groups of wheels are driven by distinct motors, it is possible to control steering of the vehicle better. For example, for a compact loader, such mechanisms make it possible to rotate the wheels in the right-side group and the wheels in the left-side group at different speeds, or even in opposite directions, which makes the vehicle very maneuverable by making it possible for it to turn around on the spot.
At least one of the displacement members of the tandem may be different from a wheel, and may, for example, be constituted by a crawler track. In particular for a loader, it is desirable to make the vehicle as compact as possible. As a result, it must be possible in a very small space, to house the various constitutive elements of the two mechanisms which serve to drive respective ones of the two tandems of wheels. The driver's seat and cab and the various controls must also be accommodated, as must the transmission assembly including in particular the pumps that serve to feed the hydraulic motors, and the motor for actuating the pumps. Hydraulic motors used in the prior art to displace this type of vehicle are generally motors of the geroller type, or axial-piston high-speed motors, coupled to stepdown gears. The driving sprockets are disposed on the outlet shaft of the hydraulic motor, and they penetrate into the chain case so that the first and second chains respectively engage them.
Such motors, with their stepdown gears and their outlet shafts are relatively bulky. Even when, to make a compact vehicle, attempts are made to dispose the motors inside the chassis of the vehicle, considerable space is required in the chassis, and the driving sprockets for the chains are cantilevered out considerably relative to the motor, so that the bearings and the shaft of the motor, have to bear very considerable stresses and have to be dimensioned accordingly.